This procedure’s success marks a new era in
skin grafting. Using this combination therapy approach many rare genetic skin
disorders can be treated in the future. The study published in
Nature magazine, sheds light on how the skin replenishes itself; and the
pertinent details of this first of a kind clinical experiment.
In 2015, a boy with a rare genetic skin
condition, called junctional epidermolysis bullosa, had lost most of his skin
and was close to death. Children with the condition have
mutations in one of three genes — LAMA3,
LAMB3 or LAMC2. Those genes produce parts of the laminin 332
protein, which helps attach the top layer of skin (the epidermis) to deeper
layer (dermis).
People with this condition
are sometimes called “butterfly children” because their skin is as fragile as
the insect’s wings. Even mild friction or bumps can cause severe blistering.
The blistering can also affect mucus membranes inside the body, making
breathing, swallowing and digesting food difficult. About 1 in every 20,000
babies in the United States is born with this condition (roughly 200 children
each year). More than 40 percent die before adolescence.
With more than 80% of the
child’s skin blistered he was being treated under the care of Dr. Tobias
Hirsch, a plastic surgeon at Ruhr University Bochum in Germany. Looking at the
severity of this child’s skin condition his team of doctors thought the boy
would also perish. Surgeons in a burn unit tried giving the boy a skin graft
from his father, but the child’s body rejected the transplant. They didn’t have
any options left to treat the child. In desperate need of help, Dr. Hirsch’s
team turned to stem cell researcher Michele De Luca of the University of Modena
and Reggio Emilia in Italy. De Luca and colleagues are famous for their cutting
edge research pioneering techniques correcting the same genetic defect. In
clinical trials, De Luca’s team had had already grown small patches of
gene-repaired skin for children with the same condition.
Together, those cases had
replaced 0.06 square meters of tissues, about the size of a piece of paper. But
the boy, who has a mutation in the LAMB3
gene, had lost nearly all the skin on his back and legs and had blistering in
other areas. The researchers needed to replace about 0.85 square meters of skin
— 14 times more.
In September 2015, the team
took a 4-square-centimeter patch of unblistered skin from the boy’s groin and
grew skin stem cells in the lab from that sample. Then De Luca and colleagues
used a retrovirus to insert a healthy copy of the LAMB3 gene into DNA in the lab-grown skin stem cells.
Those genetically corrected
skin cells grew into sheets that surgeons grafted onto the boy’s body in two
surgeries in October and November 2015. After one more surgery to replace small
patches of skin, he was released from the hospital in February 2016.
To save the life of this young boy who lost most of his skin (left, red), researchers took a small bit of his remaining skin (gray) and grew skin stem cells in the lab. Researchers then used a retrovirus to insert a healthy copy of the LAMB3 gene, needed to help keep skin layers attached, into the stem cells’ DNA. Several types of progenitor stem cells (purple, yellow) were present in the lab-grown skin cells, along with long-lived holoclones (pink). Sheets of lab-grown cells were transplanted to the boy. As the skin replenished itself, the holoclones gradually took over, suggesting a small number of stem cells are responsible for growing all the skin.
The kid is now back in school,
playing soccer, and leading a healthy life. His new skin is fully functional.
He still has some blistering in untreated areas, and his doctors are
considering replacing more skin. Meanwhile, some of the corrected stem cells
may be making their way into the boy’s untreated epidermis, and may eventually
replace all of his skin. But researchers can’t take many samples of his skin to
find out. “He’s a patient,” says De Luca. “He’s not a mouse.”
The case is a landmark in
stem cell therapy, says stem cell researcher Elaine Fuchs of Rockefeller
University in New York City. “It makes considerable headway in resolving a
brewing controversy in the epidermal stem cell field” over exactly how the skin
regenerates, she says.
One possibility is that a
large number of stem cells populate the skin. Each stem cell can then either
copy itself or morph into a variety of different types of mature skin cells.
The other possibility is that only a small number of long-lived stem cells —
known as holoclones — give rise to short-lived progenitor cells that are
forerunners to mature skin cells.
Looking At the microscope
images of the child’s skin before and after the genetically engineered skin grafts
we see that in normal skin (left) the top layer, called the epidermis (purple
in bottom images), is fused to the dermis by laminin 332 (green, in top images)
and other proteins. When a 7-year-old boy was admitted to the hospital, he’d
lost most of his skin (bottom middle, arrows show where the epidermis is
peeling away from the dermis). Mutations in the LAMB3 gene prevented the boy
from making laminin 332 protein (top middle, white dashed line indicates where
the protein should be), which helps fuse skin layers together. Gene therapy
(right panels show the boy’s skin 21 months after therapy) restored laminin 332
(top, green) and his skin stopped blistering (bottom).
When researchers inserted the
LAMB3 gene, it landed in different places in each lab-grown stem cell. De Luca
and colleagues used the different insertions like little bar codes to track the
boy’s holoclones and other skin cells. At first, his skin was a patchwork of
skin cells, with about 91 percent of progenitor cells having different
insertions than the holoclones. After four months, only 37 percent of the
progenitor cells were different from the holoclones. That indicates that most
of the progenitor cells had died and were replaced by offspring of the
long-lived holoclones. The data indicate that a small number of stem cells
replenish the skin.
While progenitor cells live
for just months, the researchers found, holoclones last a person’s lifetime.
Those findings suggest that researchers need to be careful to nurture
holoclones when growing skin in the lab, De Luca says.
This is a story of hope, accomplishment
and scientific triumph over genetic skin diseases. The possibilities to take
this work and apply it to newer indications look reassuringly bright. Being a
dermatologist I feel especially inspired, as so many patients are going to reap
benefits of this colossal medical break through.
